Liquid spall in laser shock-loaded Tin melted on compression or on release

In a metal shocked above its melting pressure or melted on release, the tensile stresses generated when the compressive pulse reflects from a free surface are induced in a liquid state. Instead of the well-known spallation process observed in solid targets, one may expect the ejection of liquid fragments from the free surface. Their formation, evolution and impact on a remote obstacle are issues of increasing interest, but very scarce data have been published on the subject yet. In this paper, we present experimental results on tin samples submitted to high pressure laser shocks, including post-test observations of the ejecta recovered after impact on a polycarbonate shield, coupled with time-resolved VISAR measurements of the free surface velocity through this shield. For shock pressures below some 80 GPa, the records can be compared to simulations involving a multi-phase equation of state. For higher loading pressures, the arrival of the shock at the free surface produces a rapid loss of reflected signal, so the particle velocity cannot be determined. In all cases, solidified fragments of tin are recovered on the shields. Their aspect indicates a very wide range of ejection velocities, and their size distribution depends significantly on shock pressure